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Nanophotonics

All‐optical control of charge‐trapping defects in rare‐earth doped oxides

Leonardo V. S. França, Shaan Doshi, Haitao Zhang, Tian Zhong

Published Feb 13, 2025• 5 citations
Publisher

Abstract

Abstract Charge‐trapping defects in crystalline solids play important roles in applications ranging from microelectronics, optical storage, sensing and quantum technologies. On one hand, depleting trapped charges in the host matrix reduces charge noise and enhances coherence of solid‐state quantum emitters. On the other hand, stable charge traps can enable high‐density optical storage systems. Here we report all‐optical control of charge‐trapping defects via optical charge trapping (OCT) spectroscopy of a rare‐earth ion doped oxide (Y 2 O 3 ). Charge trapping is realized by low intensity optical excitation in the 200–375 nm range. Charge detrapping or depletion is carried out by optically stimulated luminescence (OSL) under 532 nm stimulation. Using a Pr‐doped Y 2 O 3 polycrystalline ceramic host matrix, we observe charging pathways via the inter‐band optical absorption of Y 2 O 3 and via the 4f‐5d transitions of Pr 3+ . We demonstrate effective control of the density of trapped charges within the Y 2 O 3 matrix at ambient environment. These results point to a viable method for controlling the local charge environment in rare‐earth doped crystals via all‐optical means, and pave the way for further development of efficient optical storage technologies with ultrahigh storage capacity, as well as for the localized control of quantum coherence in rare‐earth doped solids.

DOI
10.1515/nanoph-2024-0635

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Abstract Charge‐trapping defects in crystalline solids play important roles in applications ranging from microelectronics, optical storage, sensing and quantum technologies. On one hand, depleting trapped charges in the host matrix reduces charge noise and enhances coherence of solid‐state quantum emitters. On the other hand, stable charge traps can enable high‐density optical storage systems. Here we report all‐optical control of charge‐trapping defects via optical charge trapping (OCT) spectroscopy of a rare‐earth ion doped oxide (Y 2 O 3 ). Charge trapping is realized by low intensity optical excitation in the 200–375 nm range. Charge detrapping or depletion is carried out by optically stimulated luminescence (OSL) under 532 nm stimulation. Using a Pr‐doped Y 2 O 3 polycrystalline ceramic host matrix, we observe charging pathways via the inter‐band optical absorption of Y 2 O 3 and via the 4f‐5d transitions of Pr 3+ . We demonstrate effective control of the density of trapped charges within the Y 2 O 3 matrix at ambient environment. These results point to a viable method for controlling the local charge environment in rare‐earth doped crystals via all‐optical means, and pave the way for further development of efficient optical storage technologies with ultrahigh storage capacity, as well as for the localized control of quantum coherence in rare‐earth doped solids.
Rare-earth-doped laser materials show strong prospects for quantum information storage and processing, as well as for biological imaging, due to their high-Q 4f↔4f optical transitions. However, the inability to optically detect single rare-earth dopants has prevented these materials from reaching their full potential. Here we detect a single photostable Pr3+ ion in yttrium aluminium garnet nanocrystals with high contrast photon antibunching by using optical upconversion of the excited state population of the 4f↔4f optical transition into ultraviolet fluorescence. We also demonstrate on-demand creation of Pr3+ ions in a bulk yttrium aluminium garnet crystal by patterned ion implantation. Finally, we show generation of local nanophotonic structures and cell death due to photochemical effects caused by upconverted ultraviolet fluorescence of praseodymium-doped yttrium aluminium garnet in the surrounding environment. Our study demonstrates versatile use of rare-earth atomic-size ultraviolet emitters for nanoengineering and biotechnological applications. The optical transitions that occur in rare-earth-doped crystals offer promise for quantum information storage and processing. Kolesovet al.report the optical detection of a single praseodymium ion residing in a crystal host by using an excited-state absorption process to enhance its fluorescence yield.
Rare earth ions (REI) in solid materials are among the leading systems for quantum technology applications. However, developing practical REI quantum devices with long-lived coherent states remains challenging due to great difficulties in growing high-quality REI materials and incomplete understanding of their decoherence mechanisms. In this work, we report a long optical coherence time of 422 ± 11 μs for the 7F0 → 5D0 transition, as well as a lifetime exceeding 30 hours for the 7F0 hyperfine spin states in Eu3+:Y2O3 optical ceramics. We identify the absence of two-level-system induced optical decoherence in short-range-ordered crystals and a decoherence mechanism caused by perturbing magnetic centers that were not detected previously below 1.5 K. Furthermore, we demonstrate coherent light storage over 5 μs by using the atomic frequency comb protocol. These results provide a promising proof-of-principle demonstration of quantum memory using Eu3+:Y2O3 optical ceramic system, highlighting its significant potential for practical quantum applications. Rare earth ions (REI) in solids are promising for quantum technologies. Here, the authors demonstrate a record optical coherence lifetime and the absence of two-level-system induced decoherence in Eu3+:Y2O3 optical ceramics. These findings advance the optimization of REI-based quantum systems and enable tailored material designs.
ABSTRACT Rare‐earth‐ion‐doped solid materials have attracted considerable interest for quantum technologies. However, achieving robust spin coherence in polycrystalline systems remains challenging due to structural disorder and limited understanding spin environments. Here, we report high‐quality : optical ceramics with optical inhomogeneous of GHz and sub‐kHz homogeneous linewidths, indicating a spectrally quiet optical environment. At cryogenic temperatures, spin‐dynamics measurements show that decoherence is strongly influenced by the surrounding nuclear spin bath. Magnetic‐field‐dependent studies, combined with radio‐frequency spectroscopy, reveal the sensitivity of spin coherence to weak magnetic perturbations and enable selective addressing of the bath spins. By applying an all‐optical Raman dynamical decoupling protocol, we substantially prolong the observed nuclear‐spin coherence decay, yielding a slow decay component of 224 ms. These results establish : ceramics as a promising platform for solid‐state quantum memories and highlight the potential of spin‐bath engineering in polycrystalline rare‐earth‐ion systems.
We present a case study on Eu 3+ -doped Y 2 O 3 transparent ceramics in which high-resolution laser spectroscopy is used as a material characterization tool. By comparing the results from coherent and incoherent optical spectroscopy with other characterization methods, we show that optical techniques can deliver supplementary information about the local environment of the activator ions in materials. Thus, high-resolution spectroscopy may be of interest for the investigation of a wider range of rare earth doped optical materials beyond materials studied for quantum information technology. The refinement of optical spectroscopy for the study of narrow optical transitions in rare earth ion single crystals has demonstrated that these techniques are extremely sensitive tools for probing the local environment of the rare earth ion. These techniques, such as photon echo experiments, have been important in developing materials for quantum information technology and spectral filtering applications. Here, we apply these techniques to transparent ceramic samples and compare the results with information gained from conventional material characterization techniques. Our present study demonstrates the high sensitivity of laser spectroscopic methods to microstructural strain and the presence of defects. In particular, the sensitivity is sufficient to detect small changes introduced by different thermal treatments in nominally equivalent materials. The results of our work show that it is possible to relate high-resolution optical measurements to defects and microstructural strain.
Atomic layer deposited (ALD) Y 2 O 3 thin films have been thoroughly investigated for optical or electronic applications. The coherent spectroscopy of lanthanide ions doped into this material has also recently attracted increasing interest in the field of quantum technologies for which they are considered promising candidates in quantum memories or as spin–photon interfaces. However, these most demanding applications require a deep control over the local positioning of the ions and their close environment in the crystalline matrix. This study focuses on the structural as well as optical properties of Eu 3+ and Er 3+ dopants in Y 2 O 3 using photoluminescence (PL), luminescence decay times, and inhomogeneous line width (Γ inh ) measurements within this particular context. While as-grown ALD films do not provide an ideal host for the emitters, we demonstrate that by optimizing the deposition conditions and using appropriate annealing post treatments narrow inhomogeneous lines can be obtained for the 7 F 0 ↔ 5 D 0 transition of Eu 3+ even for nanoscale films. Furthermore, about 1.5 ms lifetime has been measured for the infrared telecom transition of Er in ultrathin films (<10 nm), which is an order of magnitude higher than in nanoparticles of the same size. These results validate optimized rare-earth-doped ALD Y 2 O 3 films as a suitable platform for photonics applications where few-nanometer-thick films with well-localized emitters are mandatory. This approach provides the first building blocks toward the development of more complex devices for quantum sensing or hybrid structures coupled with other systems such as two-dimensional materials.
Ultralong-lived Coherent States in Eu3+^{3+}3+:Y2_22​O3_33​ Optical Ceramics for Quantum Memories
Rare earth ions (REI) in solid materials are among the leading systems for quantum technology applications. However, developing practical REI quantum devices with long-lived coherent states remains challenging due to great growth difficulties of high-quality REI materials and a lack of comprehensive understanding of REI's decoherence mechanisms. Here we realize a record optical coherence time of 421.5 ±\pm± 10.5 μμμs for the 7^77F0→5_0\rightarrow^50​→5D0_00​ transition and more than 30 hours lifetime for the 7^77F0_00​ hyperfine spin states in Eu3+^{3+}3+:Y2_22​O3_33​ optical ceramics. We report the elimination of two-level-system induced optical decoherence in short-range ordered crystals. Meanwhile, a new decoherence mechanism caused by new kinds of perturbing magnetic centers is identified below 1.5 K. We further demonstrate the coherent light storage over 5 μμμs by using the atomic frequency comb protocol. These results open up prospects for the realization of practical quantum memories and large scale quantum communications with REI optical ceramics.